The expression “digital pneumatic position regulator” used in this disclosure represents a mechatronic system which moves a pneumatic drive to a specific position corresponding to one or more input signals. A regulator is not necessarily used for this purpose. In order to operate, the digital pneumatic position regulator requires pressurized gas as auxiliary energy and electrical energy.
The digital pneumatic position regulator which forms this genus has at least the core components that are described in more detail in the following text. A pneumatic system is used to deliberately ventilate or vent the chambers of a single-acting or double-acting pneumatic drive as a function of one or more input signals. The movements and positions of the actuating member are represented as one or more signals with the aid of a position feedback sensor system. Furthermore, control electronics are provided, which have a microcontroller and receive one or more input signals. The firmware in the control electronics processes the input signals and the signals from the position feedback sensor system to form output signals which are used as input signals for the pneumatic system.
The pneumatic system of the digital position regulator essentially comprises a control stage and an amplifier stage. The control stage comprises one or more nozzle/bounce-plate systems. Each nozzle/bounce-plate system converts an electrical—digital, discrete or analog—input signal to a position of the bounce plate with respect to the nozzle, and thus produces an output pressure which is proportional to the position. The amplifier stage uses the output pressures of the nozzle/bounce-plate systems as a control pressure, in order to move and position one or more pneumatically controlled valves, which is or are subject to a characteristic, on its or their valve characteristic. The pneumatically controlled valves which are subject to a characteristic are closed, or are open by an amount which is proportional to the control pressure, as a function of the control pressure. The pneumatically controlled valves which are subject to a characteristic ventilate or vent the chambers of a pneumatic drive.
For single-acting and double-acting pneumatic drives, the amplifier stage has a different number of pneumatically controlled valves, which are subject to a characteristic, by means of which the position regulator deliberately ventilates or vents the connected pneumatic drive. FIG. 1 shows the principle of double-acting pneumatics for a position regulator.
If the nozzle/bounce-plate systems do not receive any input signal, or receive an invalid input signal, the pneumatic system is set to a defined behavior. In this case, a distinction is drawn between a blocking behavior and a venting behavior. In the case of a blocking behavior, all of the pneumatically controlled valves which are subject to a characteristic of the amplifier stage are closed, as a result of which the pneumatic drive is neither ventilated nor vented. In the case of a venting behavior, a distinction is drawn between single-acting and double-acting pneumatic drives. In the case of single-acting pneumatic drives, the pneumatically controlled valves which are subject to a characteristic are controlled such that the chamber of the pneumatic drive is vented. In contrast, in the case of double-acting pneumatic drives, the pneumatically controlled valves which are subject to a characteristic are controlled such that one chamber of the pneumatic drive is vented and the second chamber of the pneumatic drive is ventilated.
The firmware of the digital pneumatic position regulator implements a function which analyzes the characteristics of the connected fitting and in the process “learns” what effect different input signals to the pneumatics have on the dynamics, such as fast or slow movement, of the fitting. Furthermore, this firmware function continuously or cyclically analyzes the extent to which the characteristics of the connected fittings change and in the process adapts the relationship between the input signals to the pneumatics and the resultant dynamics.
Nozzle/bounce-plate systems are known in which the bounce plates are in the form of piezo bending bars. A piezo-immanent characteristic is to maintain the charge even in the event of failure of the power supply. For a piezo bending bar, this means that the charge which produces the bending force is maintained, and that the piezo bending bar is thus locked in a defined shape, specifically that which corresponds to the most recently applied energy.
Furthermore, digital pneumatic position regulators implement a number of special functions in their software/firmware. One of these special functions is the so-called set-value ramp. In this function, a change in the input signals which recalls a sudden change in the set position of the pneumatic drive is converted internally within the position regulator software to a ramp. This function is used whenever excessively fast closing or opening of the actuating member which is regulated by the position regulator would have a negative influence on the process or installation. One example of these negative influences is water-hammering, whose effect may even lead to mechanical failure.
One problem of the known digital pneumatic position regulator is that the characteristics which are implemented in the software are lost as soon as the electrical power supply to the position regulator, and therefore both its microcontroller and the input signals for the pneumatics, fail. In the case of a position regulator which vents in the event of failure of the electrical power supply, this results in the pneumatic drive moving in an uncontrolled manner and therefore inevitably in the negative influences which are avoided by the set-value ramp as described above.